Previously, kpdata would be a snapshotted view of the profiler queue. This
was a pain, and it didn't help with anything. Instead, now we just drain
the profiler queue directly.

This is also a nice step towards having multiple profilers, instead of the
existing global profiler. When you open kpctl, the chan has a reference on
a profiler. That happens to be the global one now. When you close the
chan, the profiler is released.